Are there any tips for editing the deform mesh cage?
If it's too hard to deal with only one cage, you could deform your mesh with 2 different cages and 2 different Mesh Deform modifiers:


Select your body mesh, enter in Edit mode and create 2 different vertex groups, one for each leg.
Create 2 different cages, each one will encage one of the 2 legs.
Give your body 2 Mesh Deform modifiers. For each modifier choose one of the cage and in the Vertex Group field, choose the corresponding vertex group you've created for each leg.
Click on the Bind buttons.
Now each cage deform only a part of the mesh.